NMR studies of pore formation and water diffusion in self-hardening cut-off wall materials

Cut-off walls for the containment of polluted sites are vertical in-ground barriers of low hydraulic cond. To construct these barriers, self-hardening watery suspensions of a special cement-based hydraulic binder and a cement-stable bentonite are used. The formation of the pore structure during hardening of suspensions with different solid contents and the water self-diffusion in the resulting cut-off wall materials were studied by non-destructive 1H NMR techniques. It was found that an increased amt. of hydrating solids in the suspension leads to a decrease in NMR relaxation times and self-diffusion coeffs. of the pore water, indicating a redn. of the pore sizes and an enhancement of the diffusion resistance. The self-diffusion coeffs. of the water in the hardened cut-off wall materials were detd. to be about four orders of magnitude smaller than in bulk liq. water and two orders of magnitude smaller than in pure bentonite-water suspensions confirming the excellent diffusive resistance of the cut-off wall materials.